Improvements for bandwidth configuration of network offering

##### ISSUE TYPE

* Improvement Request

##### COMPONENT NAME

Network offerings

##### CLOUDSTACK VERSION
~~~
4.20.0.0
~~~

##### OS / ENVIRONMENT

Ubuntu 22.04 (if relevant)
mysql 8

##### SUMMARY

All default network offerings are shown in UI as having 200Mb/s network rate. I created my own network offering without specifying network rate, and it's also shown in UI as having 200Mb/s.
Then I checked database and found that no network offering has a positive value in `network_offerings` table. All System ones have 0, while all other (default) ones have NULL.
But then, when I checked xml of Virtual router (I use isolated network with nat, if relevant again), I found this definition on my external network
```

```
That is 25Mb/s.

After I set network rate to 65K in my network offering, it become consistent at least between DB and CloudStack UI, VR then got
```




```
And another, minor, issue on the way - mysql defines the field as smallint:
`nw_rate smallint unsigned DEFAULT NULL COMMENT 'network rate throttle mbits/s'`
that does not allow values larger than 65K (worth adding an info on this to UI of creating network offering).
Modern networks can work on a larger speeds (e.g. 800Gb/s). Besides would be nice to be able not to limit it at all.

Thanks,
Alex.

まず、UI でネットワークオファリングがどのように表示されるか、また network_offerings.nw_rate がどのように保存・解釈されるかを追跡します。これらの値を virtual-router XML で出力される帯域幅と比較し、未設定の値と高レートの値が一貫して処理されることを完了条件として定義します。これには、制限または無制限の帯域幅についての明確な UI ガイダンスも含めます。

索引モデルが issue の本文から書いたものです。